1. Field of the Invention
The present invention relates to a displacement measuring apparatus comprising a scale and a receiving device array which are disposed so as to be relatively movable and output displacement signals.
2. Description of the Related Art
In the prior art, it is known to compose an optical encoder which has a light detector array serving as an index grating. For example, in such a case that 4-phases displacement signals are to be output, the light detector array may be composed of a plurality of light detectors arranged at a pitch of 3xcex/4 (where, xcex is a scale grating pitch). In this case, the respective light detectors in the same phase are connected in parallel with each other, whereby 4-phases signals of A, BB, B and AB can be output.
To produce an optical encoder with a miniaturized scale pitch, it is necessary to form a light detector array on which light detectors are arranged with a miniaturized pitch. As a result of such miniaturization, contamination, etching residue, and the like disposed on the space between the light detectors result in such an accident as to short-circuit the light detectors, or increase leakage current. These short-circuit and the leakage current reduce the reliability and through-put of the encoder. In addition, when the width of the light detector is miniaturized, signal wire contact may be defective. This also results in reducing the reliability of the encoder.
An object of the present invention is, considering the above-described situation, to provide a displacement measuring apparatus which has a high reliability and a high through-put.
The displacement measuring apparatus according to the present invention comprises: a scale on which an scale grating is formed along a measurement axis to have a grating pitch of xcex; and a receiving device array disposed against the scale to be relatively movable along the measurement axis, which detect the scale grating to output a plurality of displacement signals having different phases from each other, wherein the receiving device array comprises, a substrate; and a plurality of receiving devices having a plurality of stripe-patterned portions and connecting portions interconnecting the stripe-patterned portions to output a plurality of displacement signals having different phases from each other, the stripe-patterned portions being arranged along the measurement axis at a pitch equal to nxcex (where, n is a positive integer).
In the present invention, one receiving device is composed of a plurality of stripe-patterned portions having the same pitch as the scale or integer times of that, and connecting portions interconnecting the stripe-patterned portions. In other words, one receiving device is composed by combining a plurality of the same phase receiving devices into one detector.
According to the above-described constitution, even if contamination, etching remnant, and the like are disposed on the space between the neighboring stripe-patterned portions in a receiving device, it does not result in such an accident as to short-circuit the receiving devices, or increase leakage current because the stripe patterned portions in the receiving device have the same phase. Therefore, the displacement signal outputs are not affected with such contamination and the like. As a result, a high reliability and a high through-put can be obtained for a miniaturized encoder.
The present invention can be, for example, applied to an optical encoder. In this case, the scale grating is an optical grating, and the receiving device array is a light detector array on which a plurality of light detectors are formed to serve as the receiving devices. Each of the light detectors has a light detecting surface continuing from the stripe patterned portions to the connecting portion, and the connecting portion serves as a signal wire contact portion. As a result, even if the width of the stripe patterned portion is narrow, the signal wire can be reliably made contact with the light detector.
In the optical encoder, the plurality of the light detectors are arranged along the measurement axis at a pitch equal to {n+(2Mxe2x88x921)/2)xcex (where, n and M are positive integers, respectively) such that each set of two light detectors output dual-phase displacement signals with reverse phases each other. Alternatively, the plurality of the light detectors are arranged along the measurement axis at a pitch equal to {n+(2Mxe2x88x921)/4)xcex (where, n and M are positive integers, respectively) such that each set of four photo-detectors output four-phase displacement signals that are 90xc2x0 phase-shifted from each other. Further, the plurality of the light detectors can are arranged along the measurement axis at a pitch equal to (n+N/3)xcex (where, n is a positive integer, and N is a positive integer except multiple of 3) such that each set of three photo-detectors output three-phase displacement signals that are 120xc2x0 phase-shifted from each other.
Further, in the present invention, the connecting portion(s) can be disposed such as to, (a) interconnect between each of the midpoints of the stripe-patterned portions, (b) interconnect between each of at least one end point of the stripe-patterned portions, or (c) interconnect between the stripe-patterned portions at a plurality points of each of the stripe-patterned portions.
The present invention can also be applied to a magnetic encoder and a capacitance-type encoder. In the former case, the scale grating is a magnetic grating which generate a periodic magnetic field with a pitch of xcex, and the receiving device array is a magnetic detector array on which a plurality of magnetic detectors are formed to serve as the receiving devices. In the latter case, the scale grating is a transferring electrode array which has a plurality of transferring electrodes arranged at the pitch of xcex, and the sensor head has a transmitting electrode and a receiving electrode array serving as the receiving device array, both of which are capacitively coupled to the transferring electrode array, the receiving electrode array having a plurality of receiving electrodes which serve as the receiving devices.